The investigators' long-term goal is to understand the mechanisms involved in the pathogenesis of membranous glomerulonephropathy (MGN). They will work with the accepted experimental model of MGN, active Heymann Nephritis (HN) of rat, and concentrate their studies on the putative autoantigen, gp330, a key participant in the mechanisms of pathogenesis. Their specific aims are: A) Identify the location and structure (amino acid sequence) of the B-cell epitopes of gp330 involved in the disease. To achieve this they will isolate gp330 proteolytic fragments reactive with autoantibodies, microsequence the fragments, localize them in gp330 sequence, clone into expression vectors the corresponding cDNA's prepared by PCR amplification, test expressed fusion proteins for autoantibodies-reactivity by immunoblotting and ELISA, and for immunogenicity by immunizing rats. They will narrow down the location of the continuous and discontinuous epitope(s) by analyzing smaller clones produced by PCR, synthesize overlapping peptides spanning the epitope regions and identify the precise amino acid sequence of autoantibodies-reactive linear epitope(s) and the sequences possibly involved in the discontinuous epitopes, and test the pathogenic potential of all of the identified epitopes. B) Test the identified sequences for tolerogenic and therapeutic potential in active HN by synthesizing the putative peptide(s) or protein fragments in larger quantities, administering these peptide/protein fragments into animals, and then assessing the disease parameters. Data from these studies will provide important new information on the structure of the B cell epitopes of gp330 involved in active HN. This knowledge will lead to 1) a greater understanding of the pathogenesis of this disease at the molecular level and, 2) possibly its treatment with specific immunomodulation.